Sorry, I dont know how to add comment, so I will post this as question. (OK, I know now, I need 50 rep. points) Will sudo /touch/forcefsck check all my HDD's/parrtion's or just the one where Ubuntu is installed?
–
Miroslav RankovićNov 23 '10 at 22:47

open up a command line, (Applications
→ Accessories → Terminal) and type

sudo touch /forcefsck

then reboot your computer. The
operating system will perform a hard
disk check (fsck) for you during
the boot.

Ram:

When the system is booting, just
after the POST (power-on self test)
screen, hit the ESC key a few times
until you see the GRUB boot menu.

You should see a list of different
Linux kernels. Right at the bottom,
there's an option captioned somethimg
like Memtest86, this will
thoroughly test your memory for
corruption (also, it will take ages).